1. Field of the Invention
The present invention is generally directed to a non invasive treatment for ocular pathology, and relates more particularly to a device and method for generating high intensity focused ultrasound onto at least one annular segment of the ciliary body of an eye affected by glaucoma.
2. Description of Related Art
In the field of ophthalmologic disease, it is well known that glaucoma is a significant public health problem, between 1 to 2% of population being suffering from this pathology, because glaucoma is a major cause of blindness.
The World health organisation considers glaucoma as the third cause of blindness in the world, responsible of 15% of declared blindness occurrences, with an incidence of 2.4 millions persons per year.
The evolution of glaucoma is slow. Glaucoma is an insidious health disease because at the first stage glaucoma is asymptomatic; the patient does not feel any pain or any visual problem. When the first visual troubles appear, lesions are commonly already large and despite irreversible.
The blindness that results from glaucoma involves both central and peripheral vision and has a major impact on an individual's ability to lead an independent life.
Glaucoma is an optic neuropathy, i.e. a disorder of the optic nerve, which usually occurs in the setting of an elevated intraocular pressure. The pressure within the eye increases and this is associated with changes in the appearance and function of the optic nerve. If the pressure remains high enough for a long enough period of time, total vision loss occurs. High pressure develops in an eye because of an internal fluid imbalance.
The eye is a hollow structure that contains a clear fluid called “aqueous humor.” Aqueous humor is formed in the posterior chamber of the eye by the ciliary body. The fluid, which is made at a fairly constant rate, then passes around the lens, through the pupillary opening in the iris and into the anterior chamber of the eye. Once in the anterior chamber, the fluid drains out of the eye through two different routes. In the “uveoscleral” route, the fluid percolates between muscle fibers of the ciliary body. This route accounts for approximately ten percent of the aqueous outflow in humans. The primary pathway for aqueous outflow in humans is through the “canalicular” route that involves the trabecular meshwork and Schlemm's canal.
With the increased pressure in the eye, the aqueous fluid builds up because it cannot exit fast enough. As the fluid builds up, the intraocular pressure (IOP) within the eye increases. The increased IOP compresses the axons in the optic nerve and also may compromise the vascular supply to the optic nerve. The optic nerve carries vision from the eye to the brain. Some optic nerves seem more susceptible to abnormally elevated IOP than other eyes.
The only therapeutic approach currently available in glaucoma is to reduce the intraocular pressure.
The clinical treatment of glaucoma is approached in a step-wise fashion. Medication often is the first treatment option except for congenital glaucoma wherein surgery is the primary therapy.
Administered either topically or orally, these medications work to either reduce aqueous production or they act to increase outflow. Currently available medications may have many serious side effects including: congestive heart failure, respiratory distress, hypertension, depression, renal stones, aplastic anemia, sexual dysfunction and death.
The commonly used medications are Prostaglandin or analogs like latanoprost (Xalatan), bimatoprost (Lumigan) and travoprost (Travatan) which increase uveoscleral outflow of aqueous humor; Topical beta-adrenergic receptor antagonists such as timolol, levobunolol (Betagan), and betaxolol which decrease aqueous humor production by the ciliary body; Alpha2-adrenergic agonists such as brimonidine (Alphagan) which work by a dual mechanism, decreasing aqueous production and increasing uveo-scleral outflow; Less-selective sympathomimetics like epinephrine and dipivefrin (Propine) which increase outflow of aqueous humor through trabecular meshwork and possibly through uveoscleral outflow pathway; Miotic agents (parasympathomimetics) like pilocarpine which work by contraction of the ciliary muscle, tightening the trabecular meshwork and allowing increased outflow of the aqueous humour; Carbonic anhydrase inhibitors like dorzolamide (Trusopt), brinzolamide (Azopt), acetazolamide (Diamox) which provide a reduction of aqueous humor production by inhibiting carbonic anhydrase in the ciliary body. The two most prescribed medications are currently topical Prostaglandin Analogs and Betablockers.
Compliance with medication is a major problem, with estimates that over half of glaucoma patients do not follow their correct dosing schedules. Fixed combinations are also prescribed extensively since they improve compliance by simplifying the medical treatment.
When medication fails to adequately reduce the pressure, often surgical treatment is performed as a next step in glaucoma treatment. Both laser and conventional surgeries are performed to treat glaucoma. Generally, these operations are a temporary solution, as there is not yet a cure which is completely satisfactory for glaucoma.
There are two different approaches to treat glaucoma: either the surgeon tries to improve aqueous humor drainage, or he tries to reduce its production.
The most practiced surgeries intended to improve the aqueous humor drainage are: canaloplasty, laser trabeculoplasty, laser peripheral iridotomy (in case of angle closure glaucoma), trabeculectomy, deep non perforating sclerectomy and glaucoma drainage implants.
The most practiced surgery intended to reduce aqueous humor production is the cyclodestruction technique. When cyclodestruction is performed with a laser, it is called cyclophotocoagulation. High Intensity Focused Ultrasound can be used to obtain a cyclodestruction.
It has been imagined using controlled ultrasonic energy in the treatment of glaucoma. “Therapeutic ultrasound in the treatment of glaucoma. I. Experimental model—Coleman D J, Lizzi F L, Driller J, Rosado A L, Chang S, Iwamoto T, Rosenthal D—PMID: 3991121 (PubMed) 1985 March; 92(3): 339-46” discloses a treatment of glaucoma applying High Intensity Focused Ultrasound (HIFU) onto the ciliary body to provide filtration and focal disruption of ciliary epithelium treating elevated intraocular pressure in a non invasive manner.
An apparatus associated to this treatment using controlled ultrasonic energy in the treatment of glaucoma is also described in U.S. Pat. No. 4,484,569.
However, such apparatus which was manufactured and distributed under the commercial name of SONOCARE was very difficult to manipulate. Moreover such apparatus allows to treat only one punctual zone at a time.
Thus each shot needs to be repeated many time to treat all the circumference of the eye and all the apparatus needs to be handled, placed and calibrated many times, thus taking a very long time (i.e. displacement of the ultrasonic means, verification of the position of the ultrasonic means with regard to the punctual region to be treated with optical and echographic sighting means, filling of the device with coupling liquid and production of a ultrasonic shot).
Moreover, tissues at the neighbourhood of the treatment area can be destroyed leading to blurred vision, eye muscle imbalance or double vision.